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Abstract

In this method, autodoping at the interface between an epitaxial layer and the supporting substrate is minimized.

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United States

Language

English (United States)

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Reducing Autodoping in Epitaxial Silicon

In this method, autodoping at the interface between an epitaxial layer and
the supporting substrate is minimized.

A major problem in semiconductor device fabrication has been the
autodoping of epitaxial silicon layers from diffused regions, normally subcollector
regions. The surface concentration of the subcollector impurity is relatively high.
When the epitaxial layer is deposited, the impurity gets redistributed in a normal
and lateral direction over the interface. This effect is particularly pronounced
when the impurity concentration on the surface is large. In the initial stages of
the epitaxial process the subcollector impurity diffuses upward out of the
substrate, doping the vapor stream and outwardly across the interface to produce
unwanted doping at the interface.

In this method, the surface concentration of the buried subcollector region 10
in device 12 is maintained at a low value, as the epitaxial layer 14 is grown. This
is accomplished by implanting region 10 by ion implantation below the surface of
the substrate 12. When the epitaxial layer 14 is grown, the implanted region will
diffuse in a direction parallel to the growth direction of the epitaxial layer.
However, the impurity concentration, as shown in B, never reaches a significantly
high value at the interface between substrate 12 and layer 14 to result in
significant autodoping.